BACKGROUND:Mixed response, where different lesions within the same patient show discordant responses to treatment, remains poorly understood. To better understand the complex effects of mixed response on patient survival, we devised three different definitions of mixed response. This retrospective analysis provides the first evaluation of the association between mixed response and survival outcomes in patients with rare cancers treated with dual checkpoint blockade using ipilimumab plus nivolumab, based on data from 52 baskets in the DART SWOG S1609 trial. METHODS:We included 438 patients with Response Evaluation Criteria in Solid Tumors (RECIST) V.1.1-measurable disease and at least two target lesions, after exclusions for ineligibility, early death, or missing data. Overall survival (OS) and progression-free survival (PFS) were compared using log-rank tests and Cox regression, stratified by basket and using a day 65 landmark. A mixed response was evaluated using three definitions: Method 1-RECIST discordance across lesions; Method 2-presence of ≥1 lesion with >5 mm increase or ≥1 with >5 mm decrease; and Method 3-same as Method 2 but with a 1 mm cut-off. RESULTS:Mixed response was significantly associated with worse OS and PFS using both Method 1 (OS: HR 1.80; PFS: HR 1.58) and Method 2 (OS: HR 1.55; PFS: HR 1.57) compared with "all SD/stable per lesion". Among patients classified as "SD by RECIST", those who exhibited a mixed per lesion response according to Method 1 had significantly worse OS (median 9.9 months (8.8-12.4)) than those with a non-mixed per lesion response (median 22.7 months (19.2-32.0)). Further stratification showed that any lesion increasing >5 mm was linked to worse outcomes (OS: HR >2.37, p<0.05). CONCLUSIONS:Mixed response was significantly associated with worse survival outcomes in patients treated with dual immune checkpoint inhibitors, even among those with RECIST-defined stable disease. Our findings suggest that the "worst"-responding lesion drives prognosis, underscoring the limitations of RECIST in capturing clinically relevant heterogeneity. This study highlights the need to incorporate lesion-level assessment into immunotherapy decision-making and provides a foundation for guiding earlier transition to the next line therapies or other therapeutic options. Future studies integrating molecular biomarkers are warranted to refine response evaluation criteria and optimize immune checkpoint inhibitor-based strategies.

BACKGROUND:ICOS (inducible T-cell co-stimulator) and ICOS ligand (ICOSL) are part of an important, complex pathway that can lead to both immune stimulation and suppression. ICOS and ICOSL have heterogeneous expression patterns between and within tumor types. METHODS:This review provides an overview of ICOS and ICOSL, their mechanisms of action, expression in cancer and other diseases, and clinical trials exploring therapies targeting ICOS. RESULTS:Because of the bidirectional immune impact of the ICOS/ICOSL signaling pathway, both ICOS agonists and antagonists are under development and evaluation in clinical trials. The majority of clinical trials have focused on the development of ICOS agonists, with only one study exploring an ICOS antagonist; there have been no clinical trials developing ICOSL agonists or antagonists in oncology. ICOS can be expressed on immune-activating effector T-cell and immunosuppressive regulatory T-cell (Tregs). Thus, it is critical to determine where and how ICOS is expressed in order to evaluate the role for agonists versus antagonists. To date, ICOS agonists have shown limited activity in patients with malignancies, perhaps because of the lack of biomarker-based trials. However, an ICOS antagonist demonstrated a 44% response rate in angioimmunoblastic T-cell lymphoma; ICOS is highly expressed on T-follicular helper cells (type of CD4 cell) and proliferation of these cells may be a pathogenic mechanism for these lymphomas. A role for the ICOS/ICOSL signaling pathway has also been implicated outside of oncology, including in viral infections such as COVID-19, and in autoimmune conditions such as asthma and systemic lupus erythematosus. CONCLUSION:Biomarker-driven approaches will be important to individualize therapy and ascertain which cancer patients will derive the greatest benefit from ICOS-directed combination therapy approaches.

ABSTRACT:Plasma cell leukemia (PCL) is rare and aggressive. Plasma cells from patients with PCL were examined using next-generation sequencing (NGS). We compared NGS data from 18 patients with PCL (peripheral blood, n = 10; bone marrow, n = 8) and 1742 multiple myeloma (MM) samples. Mutations of TP53, CCND1, and KRAS were commonly observed in both diseases. Alterations in DIS3 (17% vs 1%), CCND2 (22% vs 15%), PIK3R1 (6% vs 0%), and MAP3K1 (6% vs 2%) were more common in PCL than in MM (P< .05). Translocations occurred in 11 (61.1%) patients with PCL; IGH::CCND1 and IGH::MYC were more frequent in PCL than in MM (22% vs 14%, P = not significant and 11% vs 1%, P< .05, respectively). Druggable aberrations in BRAF, CCND1, PIK3R1, and RAS may be targeted in biomarker-driven therapeutic clinical trials.

With multiple molecular targeted therapies available for patients with cancer that correspond to a specific genetic alteration, the selection of the best treatment is essential to ensure therapeutic efficacy. Molecular tumor boards (MTBs) play a key role in this process to deliver personalized medicine to patients with cancer in a multidisciplinary manner. Historically, personalized medicine has been offered to patients with advanced cancer, but the incorporation of molecular targeted therapies and immunotherapy into the perioperative setting requires clinicians to understand the role of the MTB. Evidence is accumulating to support feasibility and survival benefit in patients treated with matched therapy.

Anaplastic thyroid cancer (ATC) is a rare and aggressive tumor with a historical median survival of less than six months. Most patients have advanced disease at the time of diagnosis. Traditional cytotoxic chemotherapy has not shown survival benefits. Molecular testing and next-generation sequencing are used to identify specific targets for patients with ATC. If positive for BRAF V600E mutation, patients can be treated with BRAF/MEK inhibitors. Other therapies include tyrosine kinase inhibitors (e.g., lenvatinib) and recently immune checkpoint inhibitors which have shown remarkable results in a subset of patients, including when used along with targeted therapy. An illustrative case of a patient with advanced BRAF-mutant ATC (respiratory failure on a ventilator) who recovered with a combination of the anti-PD1 nivolumab and the BRAF V600E targeted drug vemurafenib is shown. Further studies using biomarker-based gene- and immune-targeted agents, including in combination, are needed in ATC.

3147 Background: The TargetCancer Foundation TCF-001 TRACK study (Target RAre Cancer Knowledge, NCT04504604) initiated on Oct 01, 2020, is a fully remote, advocacy-driven decentralized precision trial seeking to evaluate the clinical impact of utilizing comprehensive genomic profiling (CGP) reviewed by a molecular tumor board (MTB) for patients (pts) with rare cancers. Methods: Pts were remotely enrolled/consented. Blood samples were collected via mobile phlebotomy and tested with FoundationOne Liquid CDx; tissue biopsies (TBx) were tested using FoundationOne CDx ± laboratory developed (LD) FoundationOne RNA or LD FoundationOne Heme. Liquid biopsy testing (LBx) included algorithmic predictions for clonal hematopoiesis (CH). MTB reviewed results and provided recommendations. Results: As of Oct 01, 2025, 230 pts from 46 US states were enrolled with evaluable results; 76% (175/230) had TBx and LBx, 22% LBx, and 2% TBx biopsies. MTB review was completed for 226 pts. Median age was 57 years (interquartile range [IQR]: 47,66); > 60 tumor types were represented: cholangiocarcinoma (35%), gastrointestinal (19%), soft tissue-related sarcomas (17%), brain (14%), and others (15%). First on-study TBx CGP (n=173) showed microsatellite instability high in 2%, homologous repair deficiency-signature in 2%, and median tumor mutational burden (TMB) of 1.3 mut/Mb (IQR: 0.8,3.6; 5 pts ≥ 10 mut/Mb). In LBx (n=57), ctDNA tumor fraction (TF) was ≥1% in 28% of pts; median blood TMB was 1.3 (IQR: 0,2.5; 1 pt ≥ 10 mut/Mb). Overall, 95% (219/230) of tumors had >1 pathogenic alteration; TBx CGP detected alterations in 96% (172/179), most frequently TP53 (35%), CDKN2A (29%), CDKN2B (21%), KRAS (19%), MTAP (17%), and TERT (14%). LBx CGP detected alterations in 85% (192/225), with tumor-derived (TD) variants in KRAS (11%), IDH1 (7%), and CDKN2A (6%). TP53 (31%) included both TD and CH variants, while DNM3TA (30%), ATM (10%), TET2 (10%), and CHEK2 (8%) were mostly CH. In brain tumors, 52 variants from 28 pts with LBx identified 45 CH, 4 germline, and 3 TD. Across all tumor types, 9% (20/230) had biomarkers for FDA-approved tissue-agnostic therapies. This includes ERBB2 amplification (2% overall), which is often correlated with HER2 immunohistochemistry positivity. LBx sensitivity for DNA tissue-detected clonal SVs and rearrangements was 85% (95% CI: 0.74,0.92) when ctDNA TF≥1%; 24% (95% CI: 0.19,0.29) when <1%. Pathogenic fusions detected by RNA sequencing were not detected by DNA in 33% of cases (9/27). Conclusions: CGP identified pathogenic alterations in nearly all rare cancer patients, with tissue-agnostic biomarkers in 9%. RNA sequencing adds diagnostic yield. CH in liquid biopsies underscores need for expert MTB interpretation. TRACK, a first-of-its-kind national decentralized trial, provides a scalable framework for equitable precision oncology access. Clinical trial information: NCT04504604 .

2022 Background: ERBB2 (HER2) alterations are associated with increased risk of brain metastases in breast cancer and non-small cell lung cancer (NSCLC). However, the relationship between ERBB2 alterations and brain metastasis across other tumor types remains unclear. We hypothesized that ERBB2 -altered tumors demonstrate increased propensity for brain metastases across multiple cancer types. Methods: Using the US-based deidentified Flatiron Health-Foundation Medicine Clinico-Genomic Database (FH-FMI CGDB), we analyzed patients with advanced solid tumors who received ≥1 line of therapy. ERBB2 alterations included pathogenic/likely pathogenic variants and amplifications. Brain/CNS metastases were identified via ICD-9/10 codes and validated against manual abstraction in NSCLC patients. Focusing on patients without brain/CNS metastases at diagnosis, we performed Cox proportional hazards analyses to evaluate time from initial diagnosis to first brain/CNS metastasis, modeling death as a competing risk. Multivariable models were adjusted for tumor types. Results: The analysis included 47,653 patients across 16 tumor types. Excluding breast/NSCLC, there were 29,272 patients: 2,149 ERBB2 -altered (7.3%) and 27,123 ERBB2 -wild type. 653 patients (30% of ERBB2 -altered patients) had mutations and 1644 patients (77%) had amplifications (some had both). In a multivariable analysis adjusting for tumor type and excluding breast/NSCLC, ERBB2 alterations independently predicted accelerated brain/CNS metastasis development (HR 1.55, 95% CI 1.29-1.86, p<0.001). In separate disease-specific Cox models, the strongest associations were observed in gastric (HR 2.33, 95% CI 1.68-3.22, p<0.001) and ovarian cancers (HR 2.52, 95% CI 1.45-4.38, p<0.001) as well as breast (HR 1.70, 95% CI 1.48-1.96, p<0.001) and NSCLC (HR 1.33, 95% CI 1.11-1.60, p=0.002). Conclusions: ERBB2 alterations predict a significantly increased risk of accelerated development of brain/CNS metastases independent of tumor types, with the strongest effects observed in gastric and ovarian cancers in addition to breast and lung cancers.

Barjesteh van Waalwijk van Doorn-Khosrovani and colleagues raise important questions about this recommendation for tumour-agnostic reimbursement of nivolumab and ipilimumab in Australia. We respectfully offer a counterpoint and endorse the broad coverage. In 2025, Pharmaceutical Benefits Advisory Committee (PBAC) proposed that prescribing nivolumab and ipilimumab be guided by clinical judgement informed by the best available evidence for undefined "immunotherapy-sensitive" advanced or metastatic cancers, and, in January 2026 made a similar recommendation for pembrolizumab. Patients with rare and ultra-rare cancers, including but not limited to angiosarcoma, alveolar soft part sarcoma, gestational trophoblastic disease, small cell carcinoma of the ovary (hypercalcemic type), and adrenocortical carcinoma, face profound unmet need. Within many of these diseases, a subset of patients derives substantial benefit from immunotherapy. For example, the SWOG DART (Dual Anti-CTLA-4 and Anti-PD-1 Blockade in Rare Tumors) trial, the largest prospective evaluation of nivolumab plus ipilimumab in rare/ultra-rare cancers, demonstrated clinically meaningful activity across multiple histologies, without biomarker selection. Notably, some patients with metastatic disease remain disease-free years after treatment, outcomes rarely achieved with chemotherapy or supportive care in refractory settings. Therefore, concerns that biomarker-agnostic approval signals an evidentiary retreat overlook both our incomplete understanding immune sensitivity and the global access limits to comprehensive genomic testing. Importantly, clinical judgement is not arbitrary; it reflects training, experience, ethical reasoning, and patient-centred decision making. The question is whether demanding perfect evidence should prevent access to potentially transformative treatment. Grounded in evidence and expertise, PBAC's decision prioritises meaningful access to effective therapy for patients with few alternatives.

Background: Anti-programmed death-1 (PD-1)/cytotoxic T lymphocyte antigen-4 antibodies are efficacious in various malignancies. The potential role of dual checkpoint inhibitors in many rare solid tumors is not established. Objectives: This study presents the results of ipilimumab–nivolumab in salivary gland neoplasm cohorts of the SWOG S1609 dual anti-CTLA-4 and anti-PD-1 blockade in rare tumors (DART) trial. Design: DART is a prospective, open-label, multicenter (1016 US sites), multi-cohort phase II trial of ipilimumab (1 mg/kg intravenously (IV) every 6 weeks) plus nivolumab (240 mg IV every 2 weeks). Methods: We performed a prospective, multicenter phase II clinical trial of ipilimumab (1 mg/kg IV every 6 weeks) plus nivolumab (240 mg IV every 2 weeks) in three salivary gland neoplasm cohorts: major and minor salivary gland and adenoid cystic cancers. Patients with adenoid cystic salivary gland tumors ( N = 26) and other salivary gland neoplasms ( N = 34) were evaluable. The most common site of origin was the parotid (31%, N = 8 adenoid cystic group; 68%, N = 23 remaining histologies). Results: In the adenoid cystic group, objective response rate (ORR), 4% (complete response (CR) 0%, N = 0; partial response (PR) 4%, N = 1); 6-month progression-free survival (PFS) and overall survival (OS), 32% (95% confidence interval (CI) 18%–57%) and 84% (95% CI 71%–100%), respectively. In the remaining histologic subtypes, the confirmed ORR was 9% (CR, 0%, N = 0; PR, 9%, N = 3); stable disease (SD) >6 months/PR/unconfirmed PR = 35%; 6-month PFS and OS, 34% (95% CI 21%–55%) and 88% (95% CI 78%–100%), respectively. The most common toxicities were fatigue (39%) and diarrhea (26%); diarrhea (8%) was the most common grade 3–4 immune-related adverse event. Conclusion: In salivary gland tumors, combined ipilimumab plus nivolumab resulted in only a 4% ORR in adenoid cystic carcinoma and 9% in all other histologies combined, though the latter showed clinical benefit (included SD >6 months) in 35% of patients. Trial registration: ClinicalTrials.gov registry: NCT02834013.

Purpose:PD-L1 and PD-L2 are inhibitory ligands that interact with PD-1 receptors, enabling immune escape. Though PD-L1 has been extensively studied, much less is known about PD-L2. PD-L2 expression could lead to incomplete blockade of the PD-1 axis by anti-PD-L1 agents and also influence activity of anti-PD-1 agents. Methods:We analyzed PD-L2 transcriptomic expression in a pan-cancer cohort (N=514; 489 patients with advanced/metastatic disease and clinical correlates available) for associations with immunomodulatory variables and outcome. Results:The most common tumors were colorectal (27% [140/514]), pancreatic (11% [55/514]), and breast cancer (9.5% [49/514]). High PD-L2 expression (≥75th RNA percentile rank) occurred in 19.5% (100/514) of patients; PD-L2 expression varied across and within tumor types. High PD-L2 independently/significantly correlated with high PD-L1, PD-1, CD4, and TIM-3 RNA levels (both as dichotomized and as linear variables), with high tumor mutational burden (TMB) (≥10 mutations/megabase), and with a breast cancer diagnosis. In 217 patients who received immune checkpoint blockade (mainly anti-PD-1-based regimens), high versus moderate/low PD-L2 predicted longer overall survival (OS) (but not progression-free survival) in univariate analysis (median 1.88 years (95% confidence interval [CI] 1.37-not estimable) versus 1.21 years (95% CI 0.95-1.54) (P = 0.02). In 272 patients who never received immunotherapy, high PD-L2 expression was not prognostic for OS. Conclusions:High PD-L2 transcripts were more common in breast cancer and associated with high expression of other immune-relevant factors: PD-L1, PD-1, CD4, and TIM-3, and with TMB ≥10 mutations/megabase. High PD-L2 levels correlated with longer OS in immunotherapy-treated patients. Trial registration:NCT02478931.

The Drug Rediscovery Protocol by K. Verkerk, et al., operationalized nationwide biomarker-guided, off-label precision oncology. Yet outcomes (15.7% response rate) mirror a decade of studies, indicating a single biomarker-drug strategy ceiling. Advancing efficacy will require customized, individualized combinations, consistent with the hallmarks of cancer complexity and the I-PREDICT (Investigation of profile-related evidence determining individualized cancer therapy) style clinical studies framework, which shows that outcomes scale with greater biomarker matching.

Background: High-grade gliomas are associated with dismal outcomes and have devastating neurologic sequelae. Standard-of-care surgery, radiation, and temozolomide yield a median survival of 14-16 months in patients with glioblastoma (GBM). Methods: We report four patients with high-grade glioma (two with GBM; one initially diagnosed with GBM, now classified as World Health Organization grade 4 IDH1-mutant astrocytoma; and one with oligosarcoma [grade 4]). Tumor next-generation sequencing (NGS) was performed for all four patients, and they were treated based on their biomarkers. Results: NGS yielded actionable alterations targeted after conventional surgery/chemoradiation therapy: imatinib (for KIT and PDGRA amplification) and bevacizumab (for KDR [VEGFR2] amplification); everolimus (mTOR inhibitor for TSC2 and PTEN loss-of-function alterations); and ivosidenib (IDH1 inhibitor for IDH1 mutations in two cases, including the oligosarcoma). Three patients remain in radiographic and clinical remission at 39+, 48, and 52+ months; the patient with oligosarcoma showed clinical and imaging response lasting 8 months. Conclusions: Our exceptional responders with high-grade gliomas suggest that biomarker-matched targeted therapy can benefit select patients with high-grade glioma and warrants prospective clinical trials.

Claudin 18.2 (CLDN18.2) is exclusively expressed on gastric mucosal cell tight junctions, with minimal expression in other healthy adult tissues. Prior studies assessed expression by immunohistochemistry, mainly membrane staining. The FDA CLDN18.2 threshold for zolbetuximab approval is ≥ 75% moderate-to-strong staining. Higher-level expression has been seen in a number of cancers, including (but not limited to) gastric, gastroesophageal junction (GEJ), pancreatic, and ovarian cancers. CLDN18.2 expression can change with treatment and can exhibit heterogeneity between tumor sites. Zolbetuximab is a recently FDA-approved anti-CLDN18.2 mAb for first-line therapy of gastric/GEJ cancers in combination with chemotherapy, based on the improvement in outcomes demonstrated in the biomarker-selected populations of the SPOTLIGHT and GLOW trials. Given limited single-agent response rates to zolbetuximab, a number of other CLDN18.2-directed therapies, including antibody-drug conjugates, chimeric antigen receptor T cells, and bispecific antibodies, are under exploration in clinical trials. Despite the expression of CLDN18.2 on the gastric mucosa, these therapies have overall been tolerable in clinical trials, albeit with the use of aggressive antiemetic regimens. Herein, we summarize CLDN18.2 expression in cancer along with clinical trials of zolbetuximab and other CLDN18.2-directed therapies. Given the variability in CLDN18.2 expression within and between tumor types, biomarker-driven approaches will be critical for patient selection in clinical trials and therapeutic approaches.

Tertiary lymphoid structures (TLSs) facilitate tumor microenvironment immune interactions. While TLSs and their associated gene signatures correlate with better response to immune checkpoint inhibitors (ICIs), the complex transcriptomic interplay/co-regulation among these factors remains under investigation. We analyzed correlations between survival and transcriptome expression (35 immunoregulatory factors associated with B/T cells and TLSs) in 217 patients with ICI-treated solid tumors. Denser correlations among B/T cell markers, immune checkpoints, and TLS-related molecules was associated with longer survival. High CXCL13 (B-lymphocyte chemoattractant) expression correlated with longer overall survival (hazard ratio [HR] 0.46 [95% CI: 0.27-0.81], p = 0.006) in 217 ICI-treated patients but not in 272 ICI-naïve patients (HR 0.85 [0.52-1.40], p = 0.519), suggesting its potential predictive/ICI-related, rather than prognostic, value. Overall, patients with highly coordinated T- and B-cell activity, checkpoints, and TLS-related molecules, and higher CXCL13 expression demonstrated prolonged survival after ICIs. Comprehensive multiomics and tumor immunomic profiling may better predict outcome after immunotherapy.

Background:Interleukin (IL)-13 can modulate tumor immunosurveillance. The interplay between IL-13 and immunotherapy outcomes has not been well elucidated. Methods:IL-13 expression was evaluated by tumor RNA sequencing (514 tumors; advanced/metastatic cancers). Transcripts were normalized to internal housekeeping genes and standardized relative to a reference population (735 tumors; 35 histologies) and ranked as percentile values: IL-13-high (75th-100th percentile) and non-high (0-74th percentile). Results:Overall, 39.7% of 514 patients were men; median age, 61 years; 489 had clinical data annotation (217 immunotherapy treated; 272, immunotherapy naïve). Eighty-three of 514 patients (16.1%) showed high IL-13 expression, which was most common in sarcomas (29.2%) and independently correlated with high expression of IL-4 (odds ratio (OR)=4.20) and IL-2Rα (OR=4.63), non-high expression of TIM3 (OR=0.40), PD-L1 negativity (OR=0.40), and microsatellite instability (OR=4.03). In the immunotherapy-naïve analysis, patients with high versus non-high IL-13 levels had shorter overall survival (OS) from metastatic/advanced disease diagnosis (median, 24.5 versus 43.3 months) (HR 1.70, 95% CI 1.15-2.52, log-rank p=0.007). Interaction analysis between IL-13 levels and immunotherapy demonstrated that, among patients with non-high IL-13, those treated with immunotherapy had significantly shorter OS versus immunotherapy-naïve patients (p<0.001), whereas patients with high IL-13 levels had no significant difference in OS between immunotherapy treatment and naive groups. Conclusion:High IL-13 RNA levels were associated with other important immunoregulatory biomarkers and were most common in sarcomas. High IL-13 expression correlated with poor OS in immunotherapy-naïve patients. The observation that immunotherapy was associated with decreased survival among patients with non-high IL-13 levels is intriguing. These findings are hypothesis-generating, require validation, and have potential implications for biomarker-driven patient stratification to enhance their translational relevance.

2633 Background: Limited prior retrospective data, primarily among patients with lung cancer, liver cancer, and melanoma, has indicated that liver metastases are associated with poorer outcomes with chemotherapy, targeted agents, and checkpoint inhibitor therapy. We used a unique clinical trial resource to evaluate whether liver and/or lung metastases were associated with outcomes among patients with rare tumors treated with combination anti-PD-1 and anti-CTLA-4 therapy. Methods: The basket trial, SWOG trial S1609 (NCT02834013, DART trial), treated 655 eligible patients without lung or liver primary cancers. Associations with progression-free and overall survival were evaluated with Cox regression models; multivariable models controlled for age at trial registration, sex, performance status, race, ethnicity, primary tumor organ. Associations with clinical benefit rate (confirmed complete and partial response or stable disease for six months or longer) and treatment-related adverse events were evaluated using Fisher’s exact test. Results: There was no significant difference in rates of grade 3 or higher treatment-related adverse events across the groups. Participants with liver metastases, with or without lung metastases, had a lower likelihood of experiencing clinical benefit (11% and 18%, respectively) compared to participants with lung but not liver metastases or participants with neither lung nor liver metastases (26% and 30%, respectively, p=0.003). On multivariable analysis, both lung and liver metastases were associated with shorter progression-free and overall survival compared to presence of neither liver nor lung metastases. Conclusions: In a diverse cohort of participants with advanced rare tumors treated with combination anti-CTLA-4 and anti-PD-1 therapy, we found that both lung and liver metastases were associated with shorter progression-free and overall survival. Multivariable Cox regression models for progression-free survival and overall survival. Covariate Progression-free survival Overall survival Lung but not liver metastases (N=175) (reference = neither liver nor lung, N=269) 1.40(1.13-1.72) 0.0019 1.24(1.00-1.55)0.053 Liver but not lung metastases N=154) (reference = neither liver nor lung, N=269) 1.73(1.38-2.17) <0.001 1.33(1.05-1.68) 0.017 Liver and lung metastases N=57) (reference = neither liver nor lung, N=269) 1.96(1.44-2.65) <0.001 1.91(1.40-2.61) <0.001 Liver but not lung metastases N=154) (reference = lung but not liver, N=175) 1.24(0.96-1.60)0.095 1.07(0.83-1.38)0.62 Liver and lung metastases N=57) (reference = lung but not liver, N=175) 1.40(1.02-1.92) 0.037 1.54(1.11-2.12) 0.009 Liver and lung metastases N=57) (reference = liver but not lung, N=154) 1.13(0.83-1.55)0.45 1.44(1.04-1.99) 0.030 Hazard ratio (95% confidence interval) p-value reported.

e15121 Background: Refractory solid tumors exhibit profound molecular and functional heterogeneity, frequently requiring repeated treatment modifications after failure of standard therapies. Single-parameter testing is insufficient to guide such iterative decision-making. Comprehensive, integrated tumor profiling may enable rational, personalized treatment iterations and sustain clinical benefit across successive lines of therapy. Methods: Patients with refractory solid tumors underwent integrated EXACTA profiling encompassing genomic alterations, gene expression, immunohistochemistry, immune biomarkers, and in-vitro chemosensitivity assays. Actionable alterations and targetable pathways were identified to guide personalized therapy across successive lines. Progression-free survival (PFS) was assessed for each EXACTA-guided line. PFS ratios (PFSr) were calculated relative to the immediately preceding line, with modified PFSr (mPFSr) applied to adjust for potential false-positive and false-negative signals. The best mPFSr per patient was used to assess clinical benefit from iterative EXACTA-guided therapy. Results: EXACTA based profiling identified a highly heterogeneous yet clinically actionable genomic landscape, with recurrent alterations in PIK3CA , EGFR , ERBB2 , KRAS , BRAF , CCND1 , and BRCA2 supporting precision-guided therapy. PD-L1-stratified analysis revealed enrichment of truncating APC mutations in PD-L1-positive tumors, whereas CTNNB1 alterations were confined to PD-L1-negative tumors. Sequential EXACTA-guided therapies derived from a single comprehensive profiling event resulted in clinically meaningful benefit across multiple treatment lines. Based on best modified progression-free survival ratios (mPFSr) achieved per patient, 60.74% of patients demonstrated mPFSr > 1.5, 68.14% achieved mPFSr > 1.3, and 68.8% achieved mPFSr > 1.25. Line-wise distributions of mPFSr, including the proportion of patients achieving mPFSr > 1.3 at each EXACTA-guided treatment line, are summarized in the Table 1. Conclusions: Integrated EXACTA profiling revealed distinct tumor biology and enabled optimized treatment strategies. Mutual exclusivity of CTNNB1 alterations in PD-L1–negative tumors and enrichment of truncating APC mutations support β-catenin–TCF4–mediated PD-L1 regulation. In refractory solid tumors, a single EXACTA profiling enabled iterative, biology-guided therapy with sustained benefit. PFS ratio gains beyond the first EXACTA-guided line demonstrate the durable clinical utility of integrated profiling, supporting improved outcomes despite disease progression. Durability of Clinical Benefit Across EXACTA-Guided Lines. mPFSr from Exacta Lines >1.5 >1.3 >1.25 L2/L1 30.43% 39.13% 39.13% L3/L2 22.22% 25.92% 22.22% L4/L3 50% 50% 50%

The class II major histocompatibility complex transactivator (CIITA) is a non-DNA-binding master regulator of major histocompatibility complex class II (MHC-II) gene expression, essential for antigen presentation and adaptive immunity. Functioning as a scaffold, CIITA recruits chromatin remodelers and transcription coactivators to form the MHC-II enhanceosome, facilitating transcriptional activation. CIITA expression is tightly regulated through four promoters and is subject to both cytokine-induced and epigenetic control. Dysregulation of CIITA underpins several immune-related disorders. Its deficiency results in bare lymphocyte syndrome, a severe immunodeficiency. Variants in the CIITA gene have been implicated in autoimmune diseases, graft rejection, and immune dysregulation. Chromosomal translocations involving CIITA are among the most common genomic alterations in some B-cell lymphomas. Additionally, pathogens such as cytomegalovirus (CMV), Epstein-Barr virus (EBV), human immunodeficiency virus (HIV), and hepatitis B virus (HBV) exploit CIITA suppression to evade immune surveillance. In oncology, epigenetic silencing of CIITA contributes to MHC-II downregulation and tumor immune evasion. Restoration of CIITA expression enhances tumor immunogenicity, T cell infiltration, and responsiveness to immunotherapy. CIITA also modulates the tumor microenvironment, influences prognosis, and has therapeutic relevance in hematologic and solid tumors. Its multifunctional role positions CIITA as a critical immune regulator and a promising therapeutic target in cancer immunotherapy, antiviral strategies, and immune modulation.

3123 Background: Rare cancers - defined as an incidence rate of less than 6 per 100,000 diagnoses per year - collectively account for close to 25% of cancer burden and represent a critical unmet clinical need. The emergence of regulatory approvals for tumor-agnostic therapies based on genomic biomarkers has expanded treatment options for these patients (pts) but clinical sequencing is not yet broadly adopted for rare cancers. Here, we assess the incidence and clinical utility of FDA-approved tumor-agnostic biomarkers in a large real-world rare cancers cohort. Methods: The Tempus Lens Platform used to query the de-identified Tempus multimodal database to analyze a cohort of 45,085 real-world pts with 615 rare cancer diagnoses. All pts had DNA (Tempus xT) and/or RNA sequencing (Tempus xR). Pts were screened for FDA-approved tumor-agnostic biomarkers, including high tumor mutational burden (TMB-H, ≥ 10 mut/Mb), high microsatellite instability (MSI-H), NTRK and/or RET fusions, BRAFV600E mutations and HER2 overexpression (IHC-3+). Pts were classified based on their reported biomarker status and treatment start of the approved targeted therapy relative to the FDA-approval date. Real-world overall survival (rwOS) was defined as the time from sample collection to death or loss to follow-up. Hazard ratios (HR) from Cox-proportional hazards models were adjusted for age, sex, race, ethnicity, and stage at p<0.05 (Wald test). Results: The median age of pts was 64 years old, 59% were female, 50% of those with documented race were white and 36% had metastatic disease. The most common diagnoses were within the genital system (25%), digestive system (23%), soft tissue (12%), brain (11%) and lung (6.5%). Of the total cohort, 13% (5,881) were positive for at least one tumor-agnostic biomarker. TMB-H was the most prevalent (10.3%), followed by HER2+ (5.5%), BRAFV600E (2.6%), MSI-H (1.9%), NTRK (0.5%) and RET (0.2%) fusions. Of 59% (3,480) of pts with recorded treatments, 33% (1,138) received the approved treatment following the approval date (tumor-agnostic biomarker-positive matched) while 64% (2,227) received other treatments (tumor-agnostic biomarker-positive unmatched). Pts with tumor-agnostic biomarker-positive matched treatments had significantly improved rwOS compared to tumor-agnostic biomarker-positive unmatched pts (HR=0.8, p=0.024) and to tumor-agnostic biomarker-negative individuals (HR=0.68, p<0.001). Conclusions: A large percent (13%) of pts with rare cancer diagnoses were found to harbor an actionable biomarker associated with an FDA-approved tumor-agnostic therapy. Pts who received therapies for approved tumor-agnostic biomarkers versus those pts with the biomarker who did not receive the matched treatment demonstrated a significant survival benefit, underscoring the importance of NGS testing to optimize treatment selection for rare cancer pts.